This invention relates to a method of producing cutting tool inserts such as surgical blades made from single crystal or polycrystalline diamond.
Diamond has successfully been used since the early 1970""s as the ultimnate material for surgical scalpels, in particular, for use in eye operations (ophrhalmology). Its hardness, strength and perfect crystalline nature allow the manufacture of cutting edges that are defect free under microscopic examination at for instance 100xc3x97magnification, as required for ophthalmology. Surgical instruments equipped with diamond scalpels outperform steel scalpels by lowering, cutting resistance and creating less deformation of the tissue being cut thus allowing better precision in the operation. This is particularly important as some operations require operating precision down to {fraction (1/100)} of a millimeter or better.
The relatively high price of natural diamond and the associated cost of processing this ultra-hard material have limited this application to certain market segments.
In recent years synthesis methods have been developed for polycrystalline diamond films at significantly lower cost than natural diamond. Even more important, it is now possible to manufacture diamond plates with a diameter of more than 10 centimeters. This makes it possible to manufacture products with much larger dimensions. Natural diamonds in sizes over, say, one centimeter are rare and very expensive. In practice, surgical scalpels are limited to sizes under 8 millimeters in length for this reason.
Although the basic properties of polycrystalline diamond make it suitable for use in surgical scalpels, the conventional methods for working monocrystalline diamond are not suitable when applied to polycrystalline material. For example, the time needed to polish a single facet on a monocrystalline scalpel is of the order of minutes. Using the same method on polycrysmlline material many hours are required thus losing the cost advantage of the material. In addition, the resulting cutting edge will fail to reach the quality required as it is extremely difficult to avoid chipping the cutting edge during the polishing process.
A practical method to shape diamond products known in the diamond industry is to laser cut the material, usually with a Nd-YAG laser beam. This method produces a typical profile as represented in FIG. 1. Referring to this figure, it can be seen that at the laser beam 10 entry side, the material edge 12 is rounded producing what is called a shoulder. When the objective is to produce a sharp cutting edge characterised by a small edge radius and an included angle of less than 60 degrees, for example, this shoulder is a disadvantage.
An alternative is to use the exit of a laser beam 14 to create a cutting edge 16 (FIG. 2). This method is the subject of EP-A-720887. This approach does produce a small edge radius and a low included angle, but the quality achieved on the exit edge is limited by irregularities in the form of waviness and a rougher facet inherent in laser cutting.
According to the present invention, a method of producing a cutting edge on a layer of ultra-hard material includes the steps of providing a plate of the material, which plate has major flat surfaces on opposite sides thereof, laser cutting the plate transverse to the major surfaces to produce two or more layers each having a cutting edge defined on a surface produced by the laser cut and exposing the cutting edge to an ion bombardment etch (also known as ion beam milling). The cutting, edge is typically defined between the surface produced by the laser cut and a major surface of the plate.
Further according, to the invention, the method includes the step of ion beam smoothing the other surface or one or both of the major surfaces of the plate prior to or after the laser cutting. It has been found that ion beam smoothing reduces the friction during cutting and can lead to an improved initial cutting edge being produced by the laser cut.
The cutting edge which is produced may be a single faceted or multifaceted curring edge. Alternatively, two or more such cutting edges may be provided. The cutting edge or edges may be straight or curved, or a combination thereof. The cutting edge may be non-symmetric or symmetric. Non-symmetric cutting edges in the context of blades are those in which one of the two intersecting surfaces forming the cutting edge is a surface of the blade itself. Symmetric cutting edges in the context of blades are edges in which neither of the two intersecting surfaces forming the cutting edge is a surface of the blade itself.